A. Field of the Invention
The present invention relates to the field of mechanisms for restraining a rotatable magnetic disc and a hub assembly within a cartridge and for sealing the cartridge, when the cartridge is not in use.
B. Background of the Invention
When not in use, a cartridge for a magnetic disc should be sealed in order to prevent the ingress of contaminants into the cartridge and to restrain the magnetic disc and the hub assembly to which the disc is clamped from freely moving around within the cartridge during handling. Such movement could possibly result in the disc striking an interior surface of the cartridge, thereby causing damage to the disc. When the cartridge is inserted into a disc-drive assembly, however, the hub and disc must be allowed to rotate while the cartridge remains stationary. It is also desirable that clean air, but not the possibly contaminated air of the external environment, be allowed to circulate between the disc-drive assembly and the cartridge.
The prior art devices have included apparatuses having a handle or door disposed near the top of the cartridge in order to press the hub and disc assembly downward to seal the cartridge and to restrain the movement of the disc when the cartridge is not in use. This, or a similar approach has been taken in U.S. Pat. Nos. 3,715,739 issued to Van Acker, 3,635,608 issued to Crouch et al., 3,526,884 issued to Buslik et al., 4,071,862, issued to Lathrop, Jr. et al., 4,084,200 issued to Adair et al., 4,106,066 issued to Kudo, and 4,184,184 issued to Hedin et al.
In U.S. Pat. No. 4,078,246 issued to Berthoux et al., a different approach has been taken. In that patent, the top and bottom of the disc container are formed by rigid but elastically deformable material. When not in use, the top and bottom of the disc container tend to push outward on flanges disposed on the hub assembly, thereby mechanically holding the disc and hub stationary and sealing the disc container. In order to use the container in a disc-drive assembly, the top and bottom sides of the disc containers are pushed inward in order to allow the hub and disc to rotate freely. This arrangement requires close tolerances in the disc-drive assembly in order to insure that the correct amount of pressure is applied at both the top and the bottom of the disc container. Since such a disc container or cartridge is typically made of plastic, plastic is essentially being used as a spring. Aside from the close tolerances required, a disadvantage to the use of plastic as a spring is that plastic is susceptible to breaking. Furthermore, stress relaxation in the plastic due to creep causes the spring force to tend to decrease with time.